The effects of the RHIC E-lenses magnetic structure layout on the proton beam trajectory Page: 3 of 5
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THE EFFECTS OF THE RHIC E-LENSES MAGNETIC STRUCTURE
LAYOUT ON THE PROTON BEAM TRAJECTORY*
X. Gu#, A. Pikin, M. Okamura, W. Fischer, Y. Luo, R. Gupta, J. Hock, D. Raparia
Brookhaven National Laboratory, Upton, NY 11973.
We are designing two electron lenses (E-lens) to
compensate for the large beam-beam tune spread from
proton-proton interactions at IP6 and IP8 in the
Relativistic Heavy Ion Collider (RHIC) . They will be
installed in RHIC IR10. First, the layout of these two E-
lenses is introduced. Then the effects of e-lenses on
proton beam are discussed. For example, the transverse
fields of the e-lens bending solenoids and the fringe field
of the main solenoids will shift the proton beam. For the
effects of the e-lens on proton beam trajectory, we
calculate the transverse kicks that the proton beam
receives in the electron lens via Opera at first. Then, after
incorporating the simplified E-lens lattice in the RHIC
lattice, we obtain the closed orbit effect with the Simtrack
The Relativistic Heavy Ion Collider (RHIC) at
Brookhaven National Laboratory has operated for a
decade. It has two rings in a horizontal plane with two
head-on beam-beam interactions (IP6 and IP8) and four
long-range beam-beam interactions.
The proton beam in the Blue ring circulates clockwise,
while that in the Yellow ring circulates anti-clockwise. In
long-range beam-beam interactions the beams are
separated vertically by 10 mm. The current beam pipe at
IP10 has a 65 mm radius.
Like in other colliders, the beam-beam interaction
limits the luminosity of RHIC's polarized proton
operation. To compensate for the large beam-beam tune
spread due to head-on proton-proton interactions at IP6
and IP8 in RHIC, we are designing two e-lenses that we
will install between the two DX dipoles at RHIC IR10.
Here, we discuss the layout of these two E-lenses first.
Figure 1: Layout of RHIC and of the E-lenses.
Furthermore, to clarify the effects of such electron
* Work supported by Brookhaven Science Associates, LLC under Contract
No. DE-AC02-98CH10886 with the U.S. Department of Energy
lenses on RHIC proton beam, we detail the layout of the
RHIC lattice that includes the simplified e-lens lattice
(Figure 1). Then, with this lattice in place, we evaluated,
via the Simtrack code, the proton beam's closed orbit, its
beta functions and tune change.
THE LAYOUT OF THE TWO ELECTRON
Each of RHIC's e-lenses has one DC electron gun, one
main superconducting magnet, one electron collector, and
a beam transport system. This beam transport system has
six solenoids, from the gun side to the collector side, viz.,
GS1, GS2, GSB, CSB, CS2, and CS1. To avoid affecting
the DC electron guns with an unwanted electromagnetic
field, we placed two DC electron guns away from the IP,
while the two collectors are located near the IP (Figure 1).
Furthermore, to compensate for head-on beam-beam
collision, it is advantageous to have the direction of the
electron beam must opposite to that of the proton beam.
This means that when the e-lenses are operating, the blue
(yellow) ring's proton beam must pass first through the
yellow (blue) electron lenses. At this time, the blue
(yellow) proton beam is being transported in the same
direction as the yellow (blue) electron beam, but
separated from it vertically by 10 mm. Then, the blue
(yellow) proton beam continues, progressing through the
blue (yellow) electron lens, so that its transport direction
is opposite that of the blue (yellow) electron beam.
Also, due to the 10 mm vertical separation between the
two proton beams, the electron beams must be separated
similarly. Two layouts of the e-lens can meet this
requirement. First, we can set the vertical center of the
two electron lenses at the same vertical position (i.e., the
centre of vacuum pipe, Y=0), and use steering magnets to
move the electron beam either up by 5mm, or down by 5
mm. Or we can achieve the same outcome mechanically,
offsetting one of the electron lenses by 5 mm up from
Y=0, and the other 5 mm down. Then, the electron beam
will interact head-on with the proton beam. The latter
approach, the mechanical one, does not entail having
magnets to move the electron beam 5 mm up and down,
and so, it is easier to control.
Figure 2 illustrates the configuration of the magnetic
structure of the two electron lenses with these constraints.
The vertical layout in Figure 2 is shown with a scale that
exaggerated the displacement. The electron beam in one
electron lens interacts head-on only with one proton
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Gu, X.; Pikin, A.; Luo, Y.; Okamura, M.; Fischer, W.; Gupta, R. et al. The effects of the RHIC E-lenses magnetic structure layout on the proton beam trajectory, article, March 28, 2011; United States. (digital.library.unt.edu/ark:/67531/metadc847186/m1/3/: accessed February 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.